Segmented fiber optic sensor and method

ABSTRACT

A fiber optic sensor for sensing the presence of an analyte has a plurality of optical fibers each of which has an analyte sensing segment and the fibers are deployed so that the analyte sensing segments are arranged in sequential offset relationship over a distance such that each segment is available for detecting the analyte over a part of the distance. This has the advantage that detection of an analyte can be spatially resolved to the location of the one or more segments that have responded to the presence of the analyte. It also has the advantage that the high attenuation of sensing segments is reduced due to the smaller distance traversed by each sensing segment. Also multiple sets of such fibers may be deployed in order to detect multiple analytes, each set being constructed for a particular analyte. Also a fiber carrying structure is shown that allows the sensing segments to be available for detection of analytes and to conduct lead portions of the fibers to and from the sensing segments. A system also employs light energy sources and detectors and a processor for determining response of a sensing segment to an analyte exposure.

FIELD

This invention relates to optical sensors and more particularly to fiberoptic sensors, which are configured to detect the presence of one ormore analytes.

BACKGROUND

Optical fibers including materials which react in the presence of ananalyte to alter the characteristics of light transmitted in the fiberare well known. U.S. Pat. No. 4,399,099 issued Aug. 11, 1983, forexample, discloses fiber optic sensors for chemical and biochemicalanalysis, which employ an energy transmissive core with one or morecoatings. The sensors are operative to modify energy passing through thecore when an analyte is present. U.S. Pat. No. 4,834,496, issued May 30,1989 also describes fiber optic sensors operating in a similar manner.

U.S. Pat. No. 6,205,263 issued May 20, 2001 describes a fiber opticsensor configured to exhibit uniform power loss along the length of thefiber optic sensors in order to achieve a predictable, preferablyuniform, response to the presence of an analyte anywhere along the fiberlength.

Fiber optic sensors designed to be operative over a long distance sufferincreasing losses as a function of length. The high optical attenuationresults in increasing difficulty in obtaining a usable signal indicativeof the presence of an analyte. Therefore, there is a need in the art forfiber optic sensors that can provide signal levels at higher levels overlonger distances. Also, if sensor surveillance is needed over a longcontinuous distance or at separated intervals over a long distance, itis desirable to be able to determine the location at which a sensingevent has occurred.

SUMMARY

This summary is intended as an introductory statement and should not betaken as a recitation or an exact statement of all inventive aspects orof the content of each claim.

Embodiments of the present invention have one or more fiber opticsensing segments which are connected or spliced into or formedintegrally with low attenuation lead portions to achieve practicalsignal levels. See the special definition of “optical fiber” and “fiber”as used herein.

In accordance with an embodiment of the present invention, a fiber opticsensor for the detection of an analyte comprises a plurality of opticalfibers. Each optical fiber has a sensing segment which has a length thatis a fraction of the total length of the optical fiber and the sensingsegments are located in offset (see the special definition of this term)positions over the length of the sensor. The sensing segments are thendeployed at positions where the detection of analyte is desired.

In one aspect the sensing segments are deployed to provide continuousdetection of one analyte over a desired distance. For example, foursensing segments, each of length L/4, may be disposed in contiguous (seethe special definition of this term) positions to detect the presence ofan analyte over the entire length L. Each of such segments is afractional portion of an optical fiber of length L where the remaining3L/4 length of the optical fiber, consisting of lead portions (see thespecial definition of this term) in each instance, has low attenuationcompared to the attenuation of the analyte-sensing segment. Theresulting bundle of (4) fibers is bundled and connected to a lightsource and a detector.

In a more general aspect of the invention the sensing segments may be ofdiffering length or of the same length. For example the length of thesensing segments may be selected to accommodate the installationconditions.

In another broad aspect, the sensing segments for a given analyte areoffset (see the special definition of this term). Such offsetconfiguration therefore includes overlapping, contiguous and spacedapart. Where apparatus is configured for more than one analyte thesensing segments for different analytes need not be offset.

The sensing segments may also be deployed to provide detection of ananalyte at selected and non-contiguous intervals over a desireddistance, that is, they may be spaced apart. The sensing segments mayhave the same or different lengths or some of each.

The optical fibers may be supported by an elongated spine and protectedby a cable sheath having openings such as a braid to allow an analyte toreach the fibers.

Light can be launched into one end of the fibers and received at theother end in transmission mode or the light may be launched and receivedat the same end of the fibers in reflection mode if a reflection elementis disposed at the opposite end of the fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative embodiment of asegmented sensor according to the invention;

FIG. 2A is a schematic diagram of an embodiment of the present inventionin which sensing segments are contiguous and/or overlapping;

FIG. 2B is a schematic diagram of an embodiment of the present inventionwhere sensing segments are not contiguous;

FIGS. 3A-3F depict alternative optical energy sources and optical energydetectors according to embodiments of the present invention;

FIG. 4A shows an embodiment of the present invention where reflectionelements are used to reflect light from light sources back to lightdetectors located at the same end of the fibers;

FIG. 4B shows an embodiment of the present invention where a singlelight source is used to transmit light into fibers having reflectionelements and the light is reflected back to a single detector located atthe same end of the fibers as the light source;

FIG. 5 is a schematic cross-sectional representation an embodiment ofthe present invention having a plurality of sensors supported by fibercarriers;

FIG. 5A shows that the embodiment depicted in FIG. 5 may be scaled tohave additional fiber carriers;

FIG. 5B shows schematically a connectorized configuration of the fibercarriers.

FIG. 5C shows a schematically a connectorized configuration of thefibers carriers with the sensing segments separated by non-sensingportions;

FIG. 5D shows an open wrap disposed around the fiber carrier;

FIG. 6 shows a cross-section of an embodiment of the present inventionhaving external analyte-sensing segments and embedded lead portions;

FIG. 7 shows a fiber carrier and fiber configuration according to anembodiment of the invention;

FIG. 8 is a schematic representation of the organization of sensors ofthe multi-carrier sensor system of FIG. 7; and

FIG. 9 shows an embodiment of the present invention that provides foranalyte detection in selected areas.

FIG. 10 shows a fiber carrier and fiber configuration according to anembodiment of the invention.

FIG. 11 shows a fiber carrier and fiber configuration according to anembodiment of the invention.

DETAILED DESCRIPTION

As used herein the following terms have the following meaning unless thecontext requires otherwise:

“optical fiber” and “fiber” refers to a functional length of one or moreoptical fibers that allows transmission of an optical signal from oneend to another end or to a reflection element and back, as such it maybe a continuous integral length of optical fiber and it may also be aseries of connected or spliced lengths of optical fiber. An opticalfiber determined by connectors or splicing is made up of portions of theoptical fiber.

“segment”, “sensing segment”, “sensor segment”, “analyte-responsivesegment” and “analyte-sensing segment” refer to a length of opticalfiber that is rendered able to react to the presence of an analyte so asto alter an optical signal sent through the optical fiber. This term,when so indicated by the context can also refer to a sensing segmentthat responds to environmental conditions such temperature and humidity.

“lead portions” and “non-analyte sensing portions” means a length ofoptical fiber not treated to react to an analyte or to have any sensingchemistry.

“offset” with reference to the relative lengthwise relationship ofsensing segments in different optical fibers means any such relationshipthat allows substantially continuous sensing surveillance over adistance, as such it includes any one or combination of sensing segmentsthat are contiguous or overlapping, each of which is also definedherein.

“contiguous” with reference to the lengthwise relationship of sensingsegments in different optical fibers means that one ends where anotherbegins so as to provide substantial (not necessarily exact-see further)continuity of surveillance over a distance. Accordingly, the termcontiguous is also intended to include the configuration where only aconnector or fusion splice or other instrumentality creates a linearspace between the end of one sensing segment on one fiber and thebeginning of another sensing segment on another fiber such that thedistance being surveilled is substantially continuous even though thereis a nominal space caused by the connector or splice or otherinstrumentality thereby being effective for detection of an analyte thatis relatively spatially spread in the local area. This is distinguishedfrom spaced-apart segments where the place or distance being surveilledby different sensing segments is intended to be distinguishable andsubstantially separated as defined below.

“overlapping” with reference to the lengthwise relationship of sensingsegments means that a portion of one occupies a distance that is alsooccupied by a portion of another but that each occupies a distance notoccupied by the other.

“spaced apart” with reference to the lengthwise relationship of sensingsegments means that there is a substantial distance between the end ofone and the beginning of another so that each segment has surveillanceof a discrete location;

“chemical” and “analyte” are synonymous when used to describe or todefine material that can be sensed by a sensing segment and are notlimited to any type of chemical.

FIG. 1 is a schematic representation of a segmented sensor in accordancewith an embodiment of this invention. The sensor is designed to sensethe presence of an analyte anywhere over an arbitrary distance L. Inaccordance with the invention, a plurality of sensor segments arearranged in offset positions such that N sensors, each of length L/Noccupy the entire distance L, however, as will be further explained thesensor segments do not have to be of equal length. In the illustrativeembodiment of FIG. 1, there are four fibers 10, 20, 30, 40 (i.e., N=4)and each fiber has an analyte-sensing segment 11, 21, 31, 41. Each fiber10, 20, 30, 40 also has one or more lead portions 15, 25 a, 25 b, 35 a,35 b, 45. Preferably (for this embodiment), the sensing segments 11, 21,31, 41 are of equal length (L/4). The remainder (3L/4) (indicated bylead portions 15, 25 a, 25 b, 35 a, 35 b, 45 in FIG. 1) of each fiber10, 20, 30, 40 is preferably optimized for light transmission. The highattenuation analyte-sensing segments 11, 21, 31, 41 having lengths ofL/4 may be spliced or otherwise coupled with the one or more leadportions 15, 25 a, 25 b, 35 a, 35 b, 45 comprising low attenuation leadportions having total lengths of 3L/4 to provide the desired sensinglength L. In the embodiment of the present invention depicted in FIG. 1,the analyte-sensing segments 11, 21, 31, 41 are shown as equal lengthand additive, that is contiguous, to extend to length L. However,alternative embodiments of the present invention may haveanalyte-sensing segments 11, 21, 31, 41 with unequal lengths. Otherembodiments of the present invention may have analyte-sensing segments11, 21, 31, 41 that overlap one or more other sensing segments of otherfibers 10, 20, 30, 40. Such an overlap is indicated by the segment 33 inFIG. 1. As discussed below, still other embodiments of the presentinvention may have equal length or unequal length analyte-sensingsegments spaced apart from one another. As also shown in FIG. 1, thefibers 10, 20, 30, 40 are connected between a light source 110 under thecontrol of a signal generator 112 and a detector 120 operative totransmit to a data acquisition system 122. A processor module 124determines from the detected signal whether there is indication that ananalyte has reacted with the detection chemistry of any of the sensorsegments. A common type of response is calorimetric. This is preferablydone by comparing the received optical energy that has passed throughthe sensor segments with the source optical energy. It is also possibleto measure the received optical energy with a previously establishedbaseline to determine change. Those skilled in the art will recognizethat other devices or means may also be used to provide optical energyto the fibers 10, 20, 30, 40 and/or receive optical energy from thefibers 10, 20, 30, 40. It should be understood that the sensor systemcan be operated in reflection mode as well as in transmission mode thatis illustrated and described. That is, optical energy may be transmittedand received at the same end of an optical fiber due to the reflectionof the optical energy as it propagates within the fiber. FIGS. 4A and 4Bshow embodiments of the present invention using optical energyreflection.

FIG. 2A illustrates the fibers of FIG. 1 in a bundled configuration, atleast at the ends thereof being adapted for ease of connection to thelight source 110 and detector 120. FIG. 2A also shows that theanalyte-sensing segments 11, 21, 31, 41 are disposed in a contiguousmanner. Also, an overlap is illustrated at 33. Consequently,analyte-sensing segments 11, 21, 31, 41 are present at each point alongthe entire distance L of the bundled configuration, which provides theability to detect analyte presence anywhere along the bundle and tospatially resolve it to the portion of the distance L occupied by thesensing segment or segments that have been exposed to the analyte. FIG.2B shows an embodiment of the present invention in which the analytesensing segments 11, 21, 31, 41 are non-contiguous such that there aregaps between the analyte sensing segments 11, 21, 31, 41 from fiber tofiber. In the configuration depicted in FIG. 2B, analyte presence can belocated at the discrete spaced-apart areas in which each of the sensingsegments 11, 21, 31, 41 are deployed.

Alternative embodiments of the present invention may use differentapparatus to implement the light source 110 and the detector 120 shownin FIG. 1. FIGS. 3A-3F depict some of the alternatives that may be usedto provide the light source 110 and/or the detector 120. FIGS. 3A-3Fshow an exemplary four fiber embodiment of the present invention, butthose skilled in the art will understand that other embodiments may haveless than four fibers or more than four fibers and also that the sensingsegments may be offset, including contiguous or overlapping or they maybe spaced-apart or any combination thereof as described above. In FIGS.3A-3F, each optical fiber 10, 20, 30, 40 has a sensing segment 11, 21,31, 41 and one or more lead portions 15, 25A, 25 b, 35 a, 35 b, 45.

FIG. 3A shows an embodiment of the present invention in which each fiber10, 20, 30, 40 is illuminated by a dedicated light source 111 and theoptical output is measured by a dedicated photodetector 121. As can beseen from FIG. 3A, N optical fibers will then require N light sourcesand N photodetectors.

FIG. 3B shows an embodiment of the present invention in which a seriesof optical splitters 141 couples light from a single light source 111into N optical fibers 10, 20, 30, 40. The optical outputs from the Noptical fibers 10, 20, 30, 40 are measured by N dedicated photodetectors121. An alternative embodiment may use an optical switch (not shown) inplace of the optical splitter.

FIG. 3C shows an embodiment of the present invention in which N lightsources 111 provide light to N optical fibers 10, 20, 30, 40. Theoutputs from the N optical fibers are combined using an N×1 opticalcoupler 151, which directs the combined optical signal to a singlephotodetector 121. Preferably, the optical signals from the lightsources are separated using Time Division Multiplexing (TDM) orFrequency Division Multiplexing (FDM).

FIG. 3D shows an embodiment of the present invention in which a singlelight source 111 and a single photodetector are used 121. A 1×N opticalsplitter 141 (a series of 1×2 optical splitters may be used, as in FIG.3B) is used to couple the single light source 111 to N optical fibers10, 20, 30, 40 and an N×1 optical coupler 151 is used to combine theoutputs of the optical fibers 10, 20, 30, 40 into a combined opticalsignal for the single photodetector 121. Preferably, an optical switch161 is used to switch the optical signals in the N optical fibers 10,20, 30, 40 to limit the photodetector 121 to receiving the opticalsignal from only one optical fiber at a time.

FIG. 3E shows an embodiment of the present invention in which N highlysensitive Mach-Zehnder interferometers are used to detect the change inthe optical signal from a coherent light source. The embodimentcomprises a single coherent light source 111 and N photodetectors 121. A1×(N+1) splitter 143 splits the light from the coherent light source 111into the N optical fibers 10, 20, 30, 40 and a reference optical fiber90. The reference optical fiber 90 may have a length different than thatof the N optical fibers 10, 20, 30, 40. The output of the referencefiber 90 is split by a 1×N splitter 145 and directed to N 2×1 opticalcouplers 153. Each 2×1 optical coupler 153 combines the output from oneoptical fiber 10, 20, 30, 40 and the reference optical fiber 90 anddirects the combined signal to a photodetector 121. The combination ofthe 2×1 optical coupler 153 and the photodetector 121 acts as aMach-Zehnder interferometer to detect changes in the optical signaldirected through the optical fiber 10, 20, 30, 40. Other embodiments ofthe present invention may use other types of interferometers. Forexample, a sensing segment can comprise a component inside a Fabry-Perotcavity or become a branch of a Michelson interferometer.

FIG. 3F shows an embodiment of the present invention in which changes inthe optical signal from a coherent light source are detected, but noseparate reference optical fiber is used. As shown in FIG. 3F, a 1×Nsplitter 141 is used to direct the light from a coherent light source111 to N optical fibers 10, 20, 30, 40. The optical signals from a pairof non-adjacent optical fibers (10 and 30, or 20 and 40) are combinedusing 2×1 optical couplers 155 and the combined signal is directed to aphotodetector 121. In this embodiment, one member of the pair serves asa reference for the other, for example fiber 30 serves as a referencefor fiber 10 and fiber 40 serves as a reference for fiber 20. Theembodiment in FIG. 3F uses only N/2 optical couplers and N/2photodetectors. In this embodiment, it is assumed that the phase of theoptical signal in non-adjacent segments does not change simultaneously,while the phase in adjacent segments may change. Hence, the output ofeach photodetector 121 will produce a signal that has a magnitude thatreflects the strength of the optical signal in each fiber 10, 20, 30, 40while the polarity of the photodetector output will indicate the fiberin which the change has occurred.

Another embodiment of the present invention uses balanced detection fromtwo non-adjacent sensing segments on different fibers. This embodimentis intensity-based. However, since the information about the phasechange is unavailable, this embodiment detects change in at least one ofthe fibers, but does not identify the affected segments.

As indicated above, alternative embodiments of the present invention mayhave the light sources and the light detectors located at the same endof the fibers, operating in reflection mode. FIG. 4A shows an embodimentof the present invention similar to the embodiment depicted in FIG. 3A.FIG. 4A shows four fibers 10, 20, 30, 40, where each fiber 10, 20, 30,40 is illuminated by a dedicated light source 111 and the optical outputis measured by a dedicated photodetector 121. However, opticalcirculators 171 are used to transmit light from each light source 111into the fibers 10, 20, 30, 40. Reflection elements 173 disposed at theend of each fiber 10, 20, 30, 40 reflect light back through the fibers10, 20, 30, 40 towards the optical circulators 171. The opticalcirculators then direct the reflected light to the photodetectors 121.

In the embodiment depicted in FIG. 4A, light is transmitted twicethrough the sensing segments 11, 21, 31, 41, once during forwardtransmission and once during reflected transmission. Hence, theembodiment depicted in FIG. 4A may provide twice the attenuation oflight than that of a similar embodiment in which the light sources 111and the photodetectors 121 are disposed at opposite ends of the fibers10, 20, 30, and 40 (e.g., the embodiment depicted in FIG. 3A) andconsequently provide increased sensitivity and an improved signal tonoise ratio.

An alternative embodiment of the present invention similar to that shownin FIG. 3D is shown in FIG. 4B. FIG. 4B shows a single light source 111and a single photodetector 121 coupled to a single optical circulator171. The optical circulator 171 transmits light from the light sourceinto an optical switch 175. The optical circulator 171 also transmitslight from the optical switch 175 to the photodetector 121. The opticalswitch 175 directs light from the light source 171 to a selected one ofthe fibers 10, 20, 30, 40. The light then radiates down the selectedfiber 10, 20, 30, 40, through the corresponding sensing segment 11, 21,31, 41, and is reflected by the reflection element 173 disposed at theend of each fiber 10, 20, 30, 40 back through the corresponding analyteresponsive segment 11, 21, 31, 41 and into the optical switch 175. Theoptical switch 175 is preferably controlled such that the timingrelationship between light launched into a selected fiber 10, 20, 30 40and the light received at the photodetector 121 is known (i.e., TimeDivision Multiplexing) so that the response seen at the photodetector121 can be related to the corresponding fiber 10, 20, 30, 40. Theembodiment shown in FIG. 4B also provides the advantage of effectivelydoubling the attenuation provided by the analyte responsive segments 11,21, 31, 41.

Other embodiments of the present invention may adopt architecturessimilar to those shown in FIGS. 3B-3C and FIGS. 3E-3F, except that thelight sources 111 and photodetectors 121 are placed at the same end ofeach fiber and a reflection element 173 is used at the opposite end ofeach fiber to reflect light back towards the end having the lightsources 111 and photodetectors 121.

FIGS. 4A and 4B show a reflection element 173 disposed at the end of thefibers 10, 20, 30, 40. Those skilled in the art understand that thereflection element 173 may be provided by many elements and devicesknown in the art. Further, the reflection element 173 may be simplyprovided by terminating (e.g. cutting) the fiber 10, 20, 30, 40 orterminating the fiber 10, 20, 30, 40 and polishing and/or furthershaping the fiber end to improve its reflection characteristics.

FIGS. 4A and 4B also show that the sensing segments 11, 21, 31 may befollowed by the one or more lead portions 15, 25 b, 35 b and thereflection element 173 deployed at the distal end of each fiber 10, 20,30, 40. However, according to some embodiments of the present invention,light transmission through the lead portions 15, 25 b, 35 b that arelocated on the other side of the sensing segments 11, 21, 31 from thelight source 111 and photodetector 121 may not be required. Therefore,according to some embodiments of the present invention, the reflectionelement 173 may be simply disposed at the end of each sensing segment11, 21, 31, 41, that is, immediately after each sensing segment 11, 21,31, 41. This configuration may decrease the light attenuation caused bylight propagation through the lead portions of the fibers.

In all of the foregoing descriptions and figures sensing segments areshown as being separate from lead portions before and after them. Themeans to separate analyte-sensing segments from lead portions is byconnection such as by use of connectors or fusion connection or otherconnection means known in the art. However, alternative embodiments ofthe present invention may comprise a fiber in which the analyte-sensingsegment is formed integrally with an adjacent lead portion albeit withsome length of gradual transition due to the fiber manufacturing processto account for the transition from an analyte-sensing segment to a leadportion. It may ultimately be practical to apply sensing chemistry as afiber is being manufacturing, which is likely to include a transitiondistance so that an optical fiber as contemplated by this descriptioncould be made from a single continuous fiber.

Therefore, in the broadest sense, an analyte-sensing segment may beeither attached by connection or be integrally made with associated leadportions.

Fibers having analyte-sensing segments may be arranged in a cableassembly or harness as shown in FIG. 5. Specifically, FIG. 5 shows across-section of a cable assembly 200 having four segmented sensors suchas those shown in FIGS. 1, 2A-2B, 3A-3F, 4A-4B. Each of the four fibers10, 20, 30, 40 is disposed on a fiber carrier comprising a cylindricalslotted spine 213; A central strength member 211 may be embedded withinthe slotted spine 213 in case the material of the slotted spine 213 isnot considered to be sufficiently strong. The slotted spine 213 ispreferably constructed such that the fibers 10, 20, 30, 40 disposedwithin the slots 217 of the slotted spine 213 will be exposed to theenvironment in which analytes are to be detected. The combination of theslotted spines 213 and the fibers 10, 20, 30, 40 in the slots 217defines a segmented cable or segmented optical fiber assembly alsoreferred to as segmented sensor 214 in which the fibers 10, 20, 30, 40are disposed lengthwise adjacently. A reticulated or foraminous covering215 that permits passage of any analyte from the outside environment tothe fibers 10, 20, 30, 40 may be used to retain the fibers 10, 20, 30,40 in the slotted spine 213. An exemplary covering 215 is an open braidcomprising glass yarn.

As shown in FIG. 5, the assembly 200 may dispose a plurality ofsegmented optical fiber assemblies 214 around a cable assembly centralstrength member 231. Hence, the cable assembly 200 may comprise multiplesegmented cables 214A, 214B, 214C, 214D each of which may carry multiplefibers. Therefore the cable assembly 200 is made up of a plurality ofsegmented optical fiber assemblies that extend in a parallel bundle.Therefore, the cable assembly 200 may provide the capability to sense ananalyte over a longer distance or with a finer distance resolution byreason of the greater number of sensing segments; and both benefits canbe realized. The cable assembly 200 may also be used to detect multipleanalytes by using analyte responsive segments that are responsive todifferent analytes. This enables a plurality of analyte sets ofsegmented optical fibers to be deployed where each analyte set hassensor segments responsive to a particular analyte and each analyte setis responsive to an analyte different from the other analyte sets sothat surveillance for several different analytes can be established bysegmented deployment. Preferably each of the segmented optical fiberassemblies 214 A-D is equipped with sensing segments in its opticalfibers for the same analyte and each of them has sensing segments thatdiffer from the others. That is, for example, segmented optical fiberassembly 214A may have optical fibers whose sensing segments are allresponsive to a first analyte while segmented optical fiber assembly214B has optical fibers whose sensing segments are all responsive to asecond analyte. The cable assembly 200 may also be constructed such thatthe analyte responsive segments (indicated by the hatching in FIG. 5)appear at different rotational orientations of the slotted spines 213 bytwisting the segmented cables around the strength member 231.

In an exemplary embodiment, the cable assembly 200 depicted in FIG. 5may have central strength members 211 comprising epoxy glass rods thateach has a nominal diameter of 1.2 mm. The optical fibers 10, 20, 30, 40may have outside nominal diameters of 250 μm and the fiber carriers 213may have outside diameters of about 5.0 mm. The covering 215 such asbraided glass yarn around each slotted spine 213 would then have anoutside diameter of about 5.5 mm. The cable assembly central strengthmember 231 may also have a central core comprising an epoxy glass rod ora rod made of glass fibers. An open wrap 235 may then be used around allof the slotted spines 213 to hold all of the fibers and the segmentedcables together. FIG. 5D shows how the open wrap 235 comprising, forexample, a glass or plastic line may be wrapped lengthwise around thecable assembly 200.

The embodiment depicted in FIG. 5 may be scaled to have any number ofsegmented cables 214. FIG. 5A shows how the embodiment can be scaled tohave six segmented cables 214.

In a preferred embodiment, each of the four segmented cables 214A-D inFIG. 5 is dedicated to a specific analyte such as hydrogen cyanide,hydrogen sulfide, chlorine gas, and nerve agent. In this case eachoptical fiber in one of the segmented cables (four segmented cablesbeing illustrated) has a sensing segmented covering its own designateddistance. The configuration of FIG. 5A can be similarly equipped withadditional sensing cables for general environmental conditions such astemperature and humidity.

In a further embodiment of the invention as hereinbefore described, foreach segmented cable (214 A-D in FIG. 5), each fiber's sensing segmentis in a fiber length bounded by connectors, while the other fibers inthat segmented cable are lead portions. This is illustrated in FIG. 5Bin which a segmented cable 400 has connectors 401, 403, 405, 407 and409. Fibers 10, 20, 30 and 40 run from connector 401 to connector 409although they do so in discrete lengths A, B, C and D between theconnectors. In each of the discrete lengths one of the fibers has itssensing segment as at 11, 21, 31, and 41, while the other fibers arelead portions. In this configuration, the sensing segments beingsubstantially contiguous, a continuous distance can be undersurveillance (it is discontinuous only to the extent of the distanceoccupied by the connectors), with the ability to determine if theanalyte is present at one or more of the areas A, B, C, and D. In thecase where a plurality of analytes is of interest, a plurality ofsegmented cables 400 is deployed, each being dedicated to a specificanalyte.

FIG. 5C shows a similar connectorized set-up 500 but with the sensingdiscrete lengths A, B, C and D being spaced-apart by any selecteddistance by the insertion of a wholly passive discrete length as, X, Y,and Z

The connectorized configurations of FIGS. 5B and 5C can be applied tothe arrangements of FIGS. 5 and 5A such that each segmented cable isbounded by connectors or splices, as 401 and 409 in FIG. 5A representingthe ends of sensing cable 214A. Similarly each of the plurality ofsensing cables 214 A-D would have ends bounded by connectors or spliceswith additional intermediate connectors representing each segmenteddistance. In the configurations of FIGS. 5-5C the sensing segments ofeach analyte set are grouped sequentially so that over a distance thefirst sensing segment for each analyte set is grouped spatially with thefirst sensing segment of the other analyte set(s) and so on for eachsensing segment in spatial order.

In another embodiment for use in a system set up for surveillance for aplurality of analytes, analyte sets of segmented fibers, each analyteset having sensing segments for a particular analyte are installed on afiber carrier. In general fiber carriers have a portion on which thesensing segments are carried such as a surface that is available to bedeployed so that it will encounter an analyte the presence of which itis in surveillance for and there is also a portion for carrying the leadportions of the fibers. The latter portion can be a surface or conduitthat is located on the fiber carrier in a place that is convenient tocarry all the lead portions and it need not be and preferably is notpositioned to encounter the analyte but rather is positioned to allow aclear and unobstructed deployment of the sensing segments. In oneembodiment, the fiber carrier has an external structure on which thefirst sensing segments, in sequential order, for each analyte set aredisposed adjacently. The fiber carrier also has a passive structure(surface or conduit or the like) on which all the lead portions aredisposed. The external structure is exposed to the environment in orderthat the sensing segments be exposed to an analyte when present whilethe passive structure can be hidden or on a reverse side where exposureto the analyte is irrelevant. FIG. 6 depicts an example of thisembodiment. FIG. 6 depicts a cross-section of an assembly 300 comprisinga slotted fiber carrier 393 with lead fiber portions 312, 313, 314, 322,323, 324, 332, 333, 334, 342, 343, 344 contained inside the slottedfiber carrier 393 in an interior conduit 345 and sensing segments 311,321, 331, 341 located in slots 395 on the external structure 399 of thefiber carrier 393. A braid 396 or other means can be used to retain thesensing segments in the slots 395. The embodiment shown in FIG. 6 mayhave a smaller diameter than the embodiment shown in FIG. 5, since theembodiment of FIG. 6 only uses a single fiber carrier for surveillancefor a plurality of analytes. Note also that the embodiment of FIG. 6allows the sensing segments 311, 321, 331, 341 to be more completelyexposed to the ambient environment, which may facilitate the detectionof chemical agents (i.e., analytes) and decrease the response time.Although slots have been shown for retaining and positioning the fiberson the carrier periphery, it will be apparent to those skilled in theart that other retaining means could be employed, for example, spacedapart pairs of posts could be embedded or molded into the carrier orsimple ties could be used to secure the fibers.

FIG. 7 depicts how the transition from a sensing segment 311 located onthe periphery of the slotted spine carrier 393 to an internally locatedlead portion 312 may be handled. FIG. 7 depicts a first fiber assembly301 coupled to a second fiber assembly 302, each of which has thestructure of the assembly 300 shown in FIG. 6. FIG. 7 shows a sensingsegment 311 located on the periphery of the first fiber assembly 301coupled to a lead portion 312 located within the conduit 345 in theslotted spine carrier 393 of the second fiber assembly 302. Similarly,FIG. 7 shows a first lead portion 334 and a second lead portion 314,both located within the conduit 345 in the slotted spine carrier 393 ofthe first assembly 301, coupled to a sensing segment 331 and a secondsensing segment 311, respectively, both located on the periphery of thesecond assembly 302.

As shown in FIG. 7, only the sensing segment (depicted by hatching) ofeach fiber is exposed, while the remainder of the fiber is buried withinthe slotted spine carrier 393 in the conduit 345. Thus, FIG. 7 depictsfour simultaneously sensing fiber segments, each responsive to adifferent sensing chemistry.

It is to be noted that the first and second fiber assemblies 301, 302are linearly adjacent so that the sensing segments on the surface offirst assembly 301 are exposed the whole length of first assembly 301;and then their lead portions are concealed in the conduit 345 in thesecond assembly 302. Additional such assemblies can be fitted so thatsensing segments for each sensing chemistry on different fibers areexposed on each assembly thereby allowing for location of analytes.Hence, fiber assemblies of optimum length may be connected together bystandard optical connectors (represented by 381 in FIG. 7). For example,each fiber assembly may be a certain length and connected together ingroups of four to provide a sensor having a length additive of theirindividual lengths (disregarding small distances occupied byconnectors).

FIG. 8 shows schematically the organization of a sensor of the typeshown in FIG. 7. Specifically, the schematic of FIG. 8 is based on theassumption that four different sensing chemistries are used withsegments 311, 321, 331 and 341 of FIG. 7. Sixteen fibers are requiredfor four segmented sensors for four analytes. Connector 381 of FIG. 8corresponds in position to the space between assembly 301 and assembly302 of FIG. 7. FIG. 8 shows that the analyte-sensing segments for thefirst sensing chemistry are denoted as element 311. The left most fiberassembly shown in FIG. 8 corresponds to the first fiber assembly 301shown in FIG. 7. FIG. 8 shows that the analyte-sensing segment 311 inthis left most assembly couples through the connector 381 to leadportions 312 in the next fiber assembly. This next fiber assemblycorresponds to the second fiber assembly 302 in FIG. 7. FIG. 7 showsthat the lead portion 312 is embedded within the conduit 345. Twoadditional connectors, connector 383 and connector 385, are required toconnect the four fiber assemblies into a complete four segment sensor.For example, each fiber assembly may be 20 meters, so that the totallength of the sensor is 80 meters.

The different analyte sets of FIGS. 6-9 are like those of FIGS. 5-5Csequentially grouped so that along a distance over which they aredeployed a spatially first sensing segment for each group is on the samefiber carrier and consequently is surveilling the same partial length ofthe distance under surveillance and similarly the next sensing segmentsin spatial order for each analyte set are grouped and so on for all thesensing segments, in spatial order.

In an experimental set up, four chemistries were used to sense thepresence of four different analytes, each requiring light of a differentwavelength. The blocks (outlined) to the left as viewed in FIG. 8represent the optical light source input; the blocks to the rightrepresent the corresponding photodetectors measuring responses toindividual chemistries.

Advantageously, the optical fibers are twisted by a relative rotation ofthe carriers with respect to one another to avoid possible stress on thesystem if the apparatus is placed along arcuate paths. This rotation isrepresented by the position of the optical fibers in the space betweenthe first fiber assembly 301 and the second fiber assembly 302 of FIG.7.

Fiber carriers according to embodiments of the present invention are notlimited to carriers with circular cross-sections. FIG. 10 shows analternative embodiment of the present invention with a fiber carrierhaving a non-circular cross-section. FIG. 10 shows a first fiberassembly 303 coupled to a second fiber assembly 304, each assembly 303,304, having a fiber carrier 305 with a rectangular cross-section. Thefiber carrier 305 has an external structure 398 on which theanalyte-responsive segments 311, 321, 331, 341 are disposed. Theexternal structure 398 proves for exposure of the analyte-responsivesegments 311, 321, 331, 341 to the environment in which analytes are tobe detected. Lead portions 312, 322, 332, 342 are disposed in a passivestructure 394 which is a cavity on the bottom of the fiber carrier 305.Other embodiments according to the present invention may disposed thepassive structure on a surface of the fiber carrier 305. While FIG. 10shows a fiber carrier 305 with a rectangular cross-section, other fibercarriers of other embodiments according to the present invention mayhave cross-sections with different shapes.

FIG. 10 also shows the transitions from the analyte-responsive segments311, 321, 331, 341 to the lead portions 312, 322, 332, 342. FIG. 10shows the analyte-responsive segment 311 of the first assembly 303coupled to lead portion 312 of the second fiber assembly 304. Similarly,FIG. 7 shows the portion 312 of the first assembly 303 coupled to theanalyte-responsive segment 311 of the second assembly 302. The couplingof segments of the first assembly 303 and the second assembly 304 may beaccomplished with coupling means 381 known in the art, such as fibercouplers connectors, fiber bonding, etc.

FIG. 11 shows an alternative embodiment of the present invention with aribbon-like fiber carrier. FIG. 11 shows a first fiber assembly 306coupled to a second fiber assembly 307, each assembly 306, 306, having afiber carrier 308 generally shaped like a ribbon. The fiber carrier 308has an external structure 399 on which both the analyte responsivesegments 311, 321, 331, 341 and the non-analyte-responsive segments 312,322, 332, 342 are disposed. The analyte responsive segments 311, 321,331, 341 and the non-analyte-responsive segments 312, 322, 332, 342 aredisposed generally parallel to each other on the external structure 399.The external structure 399 proves for exposure of the analyte responsivesegments 311, 321, 331, 341 to the environment in which analytes are tobe detected and also provides a carrying surface for the non-analyteresponsive segments 312, 322, 332, 342.

FIG. 11 also shows the transitions from the analyte responsive segments311, 321, 331, 341 to the non-analyte responsive segments 312, 322, 332,342. FIG. 11 shows the analyte responsive segment 311 of the firstassembly 303 coupled to the non-analyte responsive segment 312 of thesecond fiber assembly 304. Similarly, FIG. 11 shows the non-analyteresponsive segment 312 of the first assembly 303 coupled to the analyteresponsive segment 311 of the second assembly 302. The coupling ofsegments of the first assembly 306 and the second assembly 307 may beaccomplished with coupling means 381 known in the art, such as fibercouplers, fiber bonding, etc.

FIG. 11 shows the analyte responsive segments 311, 321, 331, 341 spacedapart from each other by the non-analyte-responsive segments 312, 322,332, 342, but other embodiments may have all of the analyte responsivesegments positioned next to each other or distributed arbitrarily in anyposition on the external structure 399. Further, while FIG. 11 shows theanalyte responsive segments 311, 321, 331, 341 at different positions onthe first assembly 306 and the second assembly 307, other embodimentsmay have the analyte responsive segments 311, 321, 331, 341 at the samepositions on each fiber assembly. The coupling means 381 would thenprovide the transition from an analyte responsive segment to anon-analyte responsive segment. Hence, an arbitrarily long ribboncarrier could be manufactured with both analyte responsive andnon-analyte responsive fibers on it, which would then be cut intoshorter fiber assembly segments (similar to that described in regard toFIG. 6). The fiber assembly segments could then be coupled by couplingmeans to provide an embodiment of the present invention similar to thatshown in FIG. 11

An embodiment of the present invention may be fabricated by producing along single harness (e.g. 5000 meters) of the type depicted in FIG. 6.That is, the embodiment comprises a braided harness with analyte sensingfibers on the outside of a fiber carrier and low attenuation lead fiberportions embedded within the carrier. The braided harness can then becut into the appropriate sensing lengths. The length may be determinedby the attenuation of the sensing fiber segments. Standard fiber opticconnectors may then be used to connect together the segments.

As described above, fiber optic sensors organized in a segmentedarrangement as shown in the figures described above may be used todetect multiple types of analytes. For example, a first set of fibersmay be coated with a coating normally comprising a cladding including acolorimetric indicator for sensing hydrogen cyanide. A second set offibers may then be coated with a coating including an indicator forsensing chlorine gas. A third set of fibers may detect hydrogen sulfideand a fourth set, a nerve agent. Hence, the combination of fibers coulddetect all of hydrogen cyanide and chlorine gas, hydrogen sulfide and anerve agent in a linearly segmented system. Preferably, the coatings arecurable using either ultra violet light or heat. The coatings may thenbe cured as they are applied to optical cores as the cores are drawn.Exemplary coatings include silicones and acrylates. According toembodiments of the present invention, the (segmented) sensors may bepackaged as shown in FIGS. 5 and 5A or 6 and 7.

The decreased attenuation provided by an embodiment of the presentinvention is shown by examining typical optical fibers known in the art.Typically, chemically sensitive optical fiber may have attenuation onthe order of 1 dB/m, while low attenuation multimode optical fiber (notchemically sensitive) may have attenuation as low as 0.04 dB/m. Eachoptical fiber of the four optical fiber embodiment (described above)requires three additional optical connectors with each connector havinga loss of about 0.1 dB. In the array shown in FIG. 1, a 1:4 opticalsplitter is used to launch the light into the four separate fibers and a4:1 optical combiner is used to combine the light for application to thephotodetector. The optical splitter and the optical combiner are eachestimated to provide an additional 1 dB of loss.

Hence, the total optical losses through a single fiber in the embodimentshown in FIG. 1 are estimated as 20 m×1 dB/m (sensing segment loss)+60m×0.04 dB/m (lead segment loss)+3×0.1 dB (connector loss)+2×1 dB(splitter/combiner loss)=24.7 dB. Hence, the total optical powerattenuation from the source to the photodetector is estimated as 24.7dB. On the other hand, if the entire optical fiber is chemicallysensitive fiber as is known in the art, the total attenuation isestimated as 80 m×1 dB/m=80 dB. Therefore, the embodiment depicted inFIG. 1 may provide 55.3 dB less attenuation than a sensing system usinga single chemically sensitive optical fiber.

An embodiment of the present invention may be used to provide forcontinuous chemical surveillance over a desired distance. As shown inFIG. 2A, a structure having multiple optical fibers may be deployed(FIG. 2A shows four fibers 10, 20, 30, 40, but more or fewer fibers maybe used in accordance with the present invention), where each opticalfiber has a sensing segment. To provide for continuous chemicalsurveillance, the sensing segments for a given chemistry should bepositioned such that the segments are offset which may includecontiguous, or overlapping. Hence, the presence of an analyte at anyposition along the structure may be detected, and spatially resolvedwithin the distance covered by one or more segments that respond to itspresence, while maintaining the low loss characteristics describedabove. This type of arrangement is particularly useful to determine thepresence of an analyte at a particular sensing segment in place at aknown location over otherwise undifferentiated distances such as forperimeter surveillance.

Another embodiment of the present invention provides for chemicalsurveillance at selected spaced-apart positions along the length of thedetecting structure (see FIG. 9). As shown in FIG. 2B, a structurehaving multiple optical fibers may be deployed (FIG. 2B shows fourfibers 10, 20, 30, 40, but more or fewer fibers may be used inaccordance with the present invention), where each optical fiber has asensing segment. However, unlike the structure depicted in FIG. 2A, thesensing segments may not be contiguous or overlapping. Instead, thesensing segments are spaced-apart, positioned at those intervals atwhich the detection of an analyte is desired, while interveningpositions use the low loss lead fiber portion discussed above. Hence,the sensing segment in one optical fiber may be spaced-apart from thesensing segments in the other optical fibers. The length of the sensingsegments may differ. Hence, the presence of an analyte at selectedpositions can be detected, while maintaining the low losscharacteristics described above. This is particularly useful instructures where sensing segments can be located at separatespaced-apart locations such as windows, doors, air intakes and the likeopenings in the structure where an attack may be targeted.

FIG. 9 depicts an embodiment of the present invention used for detectinganalytes in separate spaced-apart physical locations. A detectingstructure comprising four fibers 10, 20, 30, 40 is disposed through fourseparate areas 901. The separate areas 901 may be separate rooms,portions of rooms, separate buildings, etc. FIG. 9 shows the sensingsegments 11, 21, 31 and 41 extending throughout an entire dimension ofseparate areas 901, but the sensing segments may extend for only aportion of the areas 901 or may extend past the areas 901, asillustrated by segment 13. The fibers may be fabricated in structuressuch as those shown in FIGS. 5, 5A or 6 and may be coupled together withoptical connectors 195. A control element 190, comprising a light source110 and a photodetector 120 both coupled to a processor 191, transmitslight into the fibers 10, 20, 30, 40 and receives light from the fibers10, 20, 30, 40. The processor 191 may be a digital signal processor thatboth controls the light generated by the light source 110 and processesthe electrical signals generated by the photodetector 120. The controlelement 190 provides an external output 192, which indicates whether ananalyte has been sensed by any of the fibers 10, 20, 30, 40 and,therefore, indicates the location of the sensed analyte. As discussedabove, an alternative embodiment may have the light source 110 and thephotodetector 120 disposed at the same end of the fibers 10, 20, 30, 40and a reflection element disposed at the distal end of the fibers.

What has been described is considered merely illustrative of theinvention. Those skilled in the art are competent to make variations andmodifications of the illustrations herein still within the spirit andscope of the invention as claimed hereinafter.

1. An apparatus for analyte surveillance over a distance comprising; aplurality of optical fibers, each optical fiber of the plurality ofoptical fibers having a sensing segment responsive to the same analyteand each sensing segment having a length and being disposed insequential lengthwise offset relationship over a distance to provide asubstantially continuous analyte sensing length over the distance. 2.The apparatus as claimed in claim 1 wherein each optical fiber has oneor more lead portions that have low attenuation relative to theattenuation of the sensing segments.
 3. The apparatus as claimed inclaim 1 wherein the number of optical fibers in the plurality of opticalfibers equals N and the distance equals L and each sensing segment has alength equal to L/N.
 4. The apparatus as claimed in claim 1 wherein saidplurality of optical fibers defines a first analyte set of a pluralityof optical fibers and further comprising one or more additional analytesets of a plurality of optical fibers, each of said first and additionalanalyte sets having sensing segments that are disposed in sequentiallengthwise offset relationship over a distance and being responsive toan analyte that is different from that of any other analyte set.
 5. Theapparatus as claimed in claim 1 further comprising; an optical energysource disposed to transmit light into the plurality of optical fibers,and an optical energy detector coupled to the plurality of opticalfibers to receive light from the plurality of optical fibers.
 6. Theapparatus as claimed in claim 4 wherein the sensing segments of eachanalyte set are spatially disposed in sequential groups.
 7. Theapparatus as claimed in claim 5 wherein the optical energy source andthe optical energy detector are coupled to proximal ends of theplurality of optical fibers with and reflective elements being disposedat distal ends of the plurality of optical fibers.
 8. The apparatus asclaimed in claim 5, wherein the optical energy source is disposed atproximal ends of the plurality of optical fibers and the optical energydetector is disposed at distal ends of the plurality of optical fibers.9. The apparatus as claimed in claim 5 wherein the optical energy sourceis selected from the group consisting of; a plurality of light sources;one or more light sources and one or more optical splitters coupled tothe one or more light sources; one or more light sources and one or moreoptical splitters coupled to receive light from the one or more lightsources and a plurality of optical switches coupled to the one or moreoptical splitters to receive light from the one or more opticalsplitters.
 10. The apparatus as claimed in claim 5 wherein the opticalenergy detector comprises a plurality of light detectors, or one or moreoptical combiners and one or more light detectors disposed to receivelight from the one or more optical combiners.
 11. The apparatus asclaimed in claim 5 further comprising one or more reference fibers andthe optical energy source comprises one or more coherent light sourcescoupled to at least one light source splitter, wherein the at least onelight source splitter transmits light to the plurality of optical fibersand the one or more reference fibers, and the optical energy detectorcomprises: a plurality of light detectors; a plurality of opticalcombiners, each optical combiner having an output coupled to acorresponding one light detector of the plurality of light detectors, afirst input coupled to a corresponding one optical fiber of theplurality of optical fibers, and a second input disposed to receivelight from the one or more reference fibers; and one or more referencefiber splitters coupled to receive light from the one or more referencefibers and to transmit light to the second inputs of the opticalcombiners.
 12. The apparatus as claimed in claim 5 wherein the opticalenergy source comprises one or more coherent light sources coupled to atleast one light source splitter and the at least one light sourcesplitter transmits light to the plurality of optical fibers and theoptical energy detector comprises a plurality of light detector andoptical combiner combinations, wherein the optical combiner of eachcombination has a first input coupled to a first optical fiber of theplurality of optical fibers and a second input coupled to a secondoptical fiber of the plurality of optical fibers and an output coupledto a light detector.
 13. The apparatus as claimed in claim 5 furthercomprising a processor coupled to the optical energy source and theoptical energy detector wherein the processor produces an output basedon detection of an analyte including identification of one or moresensing segments that responded to an analyte.
 14. The apparatus asclaimed in claim 6 further comprising; each optical fiber having atleast one lead portion extending from a terminal end of the sensingsegment having low attenuation relative to the attenuation of thesensing segment; and a plurality of sequentially disposed fiber carriershaving a sensor support structure and a lead support structure and thesensing segments of each analyte set are spatially disposed insequential groups on the sensor support structure and the lead portionsof each set are disposed on the lead support structure whereby the fibercarrier may be deployed so that the sensor support structure can beexposed to an analyte whose presence is under surveillance and the leadsupport structure need not be disposed for exposure to analytes.
 15. Theapparatus of claim 6 further comprising a plurality of elongate fibercarriers disposed sequentially, each fiber carrier having an internalconduit and an external structure and each optical fiber having one ortwo lead portions extending from a single one of or both terminal endsof the sensing segments each of the plurality of fibers being fitted tothe plurality of fiber carriers such that its sensor segment is retainedon the external structure of one fiber carrier and the one or both leadportions are carried in the internal conduits of the one or more otherfiber carriers whereby the sensing segment of each of the fibers is onthe external structure of one fiber carrier and all lead portions of thefibers are in the conduit or conduits of one or a plurality of otherfiber carriers whereby the fiber carriers having sensing segments ontheir external structure may be disposed at each of a plurality ofdesired locations thereby to be in surveillance at the plurality oflocations for an analyte or analytes.
 16. The apparatus as claimed inclaim 8 wherein the optical energy source comprises a plurality of lightsources, at least one light source for each optical fiber, and theoptical energy detector comprises a plurality of photodetectors, atleast one photodetector for each optical fiber, and each optical fiberhas at least one light source and at least one photodetector coupled tothe proximal end of the optical fiber through one of the one or moreoptical circulators.
 17. The apparatus as claimed in claim 8 wherein theoptical energy source comprises one or more light sources and theoptical energy detector comprises one or more photodetectors and one ormore optical switches couple the one or more optical circulators to theproximal ends of the plurality of optical fibers.
 18. The apparatus asclaimed in claim 14 further comprising optical connectors or opticalsplices coupling the portions of optical fibers disposed on each fibercarrier to the portions of optical fibers in an adjacent fiber carrier.19. The apparatus as claimed in claim 15 wherein the fiber carrier iscircular in cross section and the outside periphery is the externalstructure and having a conduit in it that is the passive structurewhereby the sensing segments are disposed on the outside periphery andthe lead portions are disposed in the conduit.
 20. The apparatus ofclaim 15 wherein a sensing segment of each of the plurality of fibers ison the external structure of each fiber carrier, sequentially.
 21. Theapparatus of claim 15 wherein intermediate fiber carriers have only leadportions in their conduits so that the fiber carriers with sensingsegments are separated by any selected number of intermediate fibercarriers that have no sensing segments.
 22. The apparatus of claim 21wherein fiber carriers having sensing segments are of a predeterminedlength appropriate to a location for surveillance and one or moreintermediate fiber carriers having only lead portions in the conduittherof are of a length to effect connection of the fiber carriers havingsensing segments.
 23. The apparatus of claim 21 further comprising; anoptical energy source disposed to transmit light into the plurality ofoptical fibers, and an optical energy detector coupled to the pluralityof optical fibers to receive light from the plurality of optical fibers.24. An apparatus for analyte surveillance at selected locationscomprising; a plurality of optical fibers, each optical fiber of theplurality of optical fibers having a sensing segment for the sameanalyte the sensing segments each having a length and being disposed insequential spaced apart relationship over a distance to provide asensing segment at each of selected locations whereby the presence ofthe analyte may be detected at one or more of the selected locations atwhich one or more sensing segments respond to the analyte presence bydetecting the response of the one or more sensing segments to thepresence of the analyte.
 25. The apparatus as claimed in claim 24further wherein said plurality of optical fibers defines a first analyteset of a plurality of optical fibers and further comprising one or moreadditional analyte sets of a plurality of optical fibers each of saidfirst and additional analyte sets having sensing segments responsive toan analyte that is different from that of any other set and beingdisposed in sequential spaced apart groups at the selected locations.26. The apparatus as claimed in claim 24 wherein each optical fiber hasone or more lead portions that have low attenuation relative to theattenuation of the sensing segments.
 27. The apparatus as claimed inclaim 24 further comprising; an optical energy source disposed totransmit light into the plurality of optical fibers, and an opticalenergy detector coupled to the plurality of optical fibers to receivelight from the plurality of optical fibers.
 28. The apparatus as claimedin claim 25 further comprising; each optical fiber having at least onelead portion extending from a terminal end of the sensing segment havinglow attenuation relative to the attenuation of the sensing segment; anda plurality of sequentially disposed fiber carriers having a sensorsupport structure and a lead support structure and the sensing segmentsof each analyte set are spatially disposed in sequential groups on thesensor support structure at the selected locations and the lead portionsof each set are disposed on the lead support structure whereby the fibercarriers may be deployed so that the sensor support structure can beexposed to an analyte whose presence is under surveillance at theselected locations and the lead support structure need not be disposedfor exposure to analytes.
 29. The apparatus of claim 25 furthercomprising a plurality of elongate fiber carriers disposed sequentially,each fiber carrier having an internal conduit and an external structureand each optical fiber having one or two lead portions extending from asingle one of or both terminal ends of the sensing segments each of theplurality of fibers being fitted to the plurality of fiber carriers suchthat its sensor segment is retained on the external structure of onefiber carrier and the one or both lead portions are carried in theinternal conduits of the one or more other fiber carriers whereby thesensing segment of each of the fibers is on the external structure ofone fiber carrier and all lead portions of the fibers are in the conduitor conduits of one or a plurality of other fiber carriers whereby thefiber carriers having sensing segments on their external structure maybe disposed at each of a plurality of desired locations thereby to be insurveillance at the plurality of locations for an analyte or analytes.30. The apparatus as claimed in claim 27 wherein the optical energysource and the optical energy detector are coupled to proximal ends ofthe plurality of optical fibers with and reflective elements beingdisposed at distal ends of the plurality of optical fibers.
 31. Theapparatus as claimed in claim 27 wherein the optical energy source isdisposed at proximal ends of the plurality of optical fibers and theoptical energy detector is disposed at distal ends of the plurality ofoptical fibers.
 32. The apparatus of claim 29 wherein a sensing segmentof each of the plurality of fibers is on the external structure of eachfiber carrier, sequentially.
 33. The apparatus of claim 29 whereinintermediate fiber carriers have only lead portions in their conduits sothat the fiber carriers with sensing segments are separated by anyselected number of intermediate fiber carriers that have no sensingsegments.
 34. The apparatus of claim 33 further comprising; an opticalenergy source disposed to transmit light into the plurality of opticalfibers, and an optical energy detector coupled to the plurality ofoptical fibers to receive light from the plurality of optical fibers.35. The apparatus as claimed in claim 34 wherein the optical energysource and the optical energy detector are coupled to proximal ends ofthe plurality of optical fibers with and reflective elements beingdisposed at distal ends of the plurality of optical fibers.
 36. Theapparatus as claimed in claim 34 wherein the optical energy source isdisposed at proximal ends of the plurality of optical fibers and theoptical energy detector is disposed at distal ends of the plurality ofoptical fibers.
 37. A method for sensing the presence of one or moreanalytes, the method comprising: disposing a plurality of optical fibersensing segments at desired locations; providing lead portions totransmit optical energy into the sensing segments; and providing leadportions to receive optical energy from the optical fiber sensingsegments the lead portions having low attenuation relative to theattenuation of the sensing segments.
 38. The method as claimed in claim37 wherein the optical fiber sensing segments are disposed on externalstructure of one or more fiber carriers.
 39. The method as claimed inclaim 37, wherein the sensing segments, the optical fiber inputsegments, and the lead segments comprise a plurality of optical fibersdisposed lengthwise adjacently and each optical fiber has one sensingsegment that is offset from the sensing segments of the adjacent opticalfibers to provide a substantially continuous analyte-sensing length overa distance.
 40. The method as claimed in claim 38 wherein one or more ofthe optical fiber input segments and/or one or more of the optical fiberoutput segments are embedded within at least one of the fiber carriers.41. The method as claimed in claim 39, wherein the number of opticalfibers in the plurality of optical fibers equals N and the distanceequals L and each sensing segment has a length equal to L/N.
 42. Themethod as claimed in claim 37, wherein the sensing segments, the opticalfiber input segments, and the lead segments comprise a plurality ofoptical fibers disposed lengthwise adjacently, wherein each opticalfiber has one or more sensing segments and the one or more sensingsegments of each optical fiber are linearly spaced apart from the one ormore sensing segments of the adjacent optical fibers, whereby there isat least one non-analyte-sensing gap between the adjacent sensingsegments.
 43. The method as claimed in claim 37, further comprisingdetecting changes in light propagating through the sensing segments withat least one interferometer.
 44. The method as claimed in claim 37further comprising bundling the sensing segments, the input leadsegments, and the output lead segments into a single fiber bundle. 45.The method as claimed in claim 37, wherein the input lead portion andthe output lead portions comprise the same physical optical fibers andthe method further comprises: receiving optical energy at a proximal endof at least one of the sensing segments; and disposing a reflectiveelement at a distal end of the at least one sensing segment.
 46. Themethod as claimed in claim 37, wherein the input lead portions and theoutput lead portions comprise the same physical optical fibers and themethod further comprises: receiving optical energy at a proximal end ofat least one of the sensing segments; coupling a proximal end of a leadportion to a distal end of the at least one sensing segment; anddisposing a reflective element at a distal end of the lead portion 47.The method as claimed in claim 37, wherein the desired locationscomprise defined areas and the method further comprises: controllingoptical energy transmission into the input lead portions; receivingoptical energy from the output lead portions; and processing thereceived optical energy to determine detection of at least one analytewithin any of the defined areas.
 48. A chemical sensing apparatuscomprising: a plurality of optical fibers, each optical fibercomprising: one or more analyte responsive segments and one or more lowloss lead portions, wherein the analyte responsive segments are disposedat desired locations; means for providing optical energy to the opticalfibers; and means for detecting optical energy propagating within theoptical fibers.
 49. The apparatus according to claim 48, wherein eachoptical fiber has one analyte-responsive segment and theanalyte-responsive segments are disposed in sequential offset lengthwiserelationship to provide a substantially continuous analyte-sensinglength over a distance.
 50. The apparatus according to claim 48, whereinthe one or more analyte-responsive segments of each optical fiber aredisposed in a sequential spaced apart lengthwise relationship to detectanalytes at different and discrete locations.
 51. The apparatusaccording to claim 48, wherein the optical fibers are disposedlengthwise adjacently in one or more fiber carriers.
 52. The apparatusas claimed in claim 48, wherein the means for providing optical energyis disposed at proximal ends of the plurality of optical fibers and themeans for detecting optical energy is disposed at distal ends of theplurality of optical fibers.
 53. The apparatus as claimed in claim 48,wherein the means for providing optical energy and the means fordetecting optical energy are disposed at proximal ends of the pluralityof optical fibers and means for reflecting optical energy is disposed atdistal ends of the plurality of optical fibers.
 54. An apparatus forsensing and locating the presence of an analyte comprising: a pluralityof optical fibers disposed lengthwise adjacently and extending eitherintegrally continuously or through connection over a determined length,wherein each optical fiber has an analyte-sensing segment of adetermined length less than the entire determined length of the opticalfiber; the analyte-sensing segments of designated adjacent ones of theoptical fibers being ordered in sequential lengthwise relationship toeach other whereby each optical fiber may sense the presence of theanalyte along the determined length of the analyte-sensing segmentthereof.
 55. The apparatus of claim 54 further wherein theanalyte-sensing segments are located relative to each other in anyselected combination of serial relationship selected from: (a) offset;and (b) spaced apart.
 56. The apparatus of claim 54 further comprising:an optical energy source disposed to transmit light into the pluralityof optical fibers; an optical energy detector coupled to the pluralityof optical fibers to receive light from the plurality of fibersdiscriminating each fiber; and means to detect a change in the receivedlight from each of the optical fibers caused by an analyte in contactwith the analyte-sensing segment of the optical fiber.
 57. An apparatusfor sensing and locating the presence of an analyte comprising; aplurality of fiber carriers, each having a plurality of peripheral fiberreceptacles extending lengthwise thereof and passive structure extendinglengthwise thereof and wherein the fiber carriers are end-to-endadjacent; a plurality of optical fibers, each optical fiber having asensing segment and at least one lead portion extending from one or bothterminal ends of the sensing segment; the sensing portion of eachoptical fiber disposed in a peripheral receptacle of a spine portion andthe lead portions of each optical fiber disposed in a passive structureof an adjacent fiber carrier.